Target Density Effects on Charge Transfer of Laser-Accelerated Carbon Ions in Dense Plasma.
Target Density Effects on Charge Transfer of Laser-Accelerated Carbon Ions in Dense Plasma.
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DOI：
10.1103/physrevlett.130.095101
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发表时间：
2022-08
影响因子：
8.6
通讯作者：
J. Ren;B. Ma;LI-RONG Liu;Wenqing Wei;Benzheng Chen;Shizheng Zhang;Hao Xu;Zhongming Hu
中科院分区：
文献类型：
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作者：
J. Ren;B. Ma;LI-RONG Liu;Wenqing Wei;Benzheng Chen;Shizheng Zhang;Hao Xu;Zhongming Hu
我们报告的电荷状态测量的激光加速的碳离子的能量范围内的几个兆电子伏穿透一个致密的部分电离等离子体。等离子体是由软X射线激光诱导空腔辐射的泡沫靶照射产生的。我们使用密度为2 mg/cm^{3}、相互作用长度为1 mm的醋酸三纤维素（C_{9}H_{16}O_{8}）泡沫作为靶材料。这种等离子体是有利的高精度测量，由于良好的均匀性和较长的寿命相比，离子脉冲长度和相互作用的持续时间。等离子体参数为T_{e}=17 eV，n_{e}=4×10^{20} cm^{-3}。我们观察到通过等离子体的平均电荷状态高于常用的半经验公式所预测的。通过求解速率方程，我们将这种增强归因于靶密度效应，靶密度效应一方面会增加电离速率，另一方面会降低电子捕获速率。基本的物理学实际上是激发态寿命与碰撞频率的平衡。在以往的测量中，部分电离等离子体从气体放电和z箍缩激光直接照射，没有目标密度的影响曾经被证明。这是第一次，我们能够实验证明，目标密度效应开始发挥重要作用，在等离子体附近的钕玻璃激光辐射的临界密度。这一发现对重离子束驱动的高能密度物理和快速点火具有重要意义。该方法为精确解决高强度短脉冲激光在稠密等离子体区的束-等离子体相互作用问题提供了一种新的方法。
We report on charge state measurements of laser-accelerated carbon ions in the energy range of several MeV penetrating a dense partially ionized plasma. The plasma was generated by irradiation of a foam target with laser-induced hohlraum radiation in the soft x-ray regime. We use the tricellulose acetate (C_{9}H_{16}O_{8}) foam of 2 mg/cm^{3} density and 1 mm interaction length as target material. This kind of plasma is advantageous for high-precision measurements, due to good uniformity and long lifetime compared to the ion pulse length and the interaction duration. We diagnose the plasma parameters to be T_{e}=17 eV and n_{e}=4×10^{20} cm^{-3}. We observe the average charge states passing through the plasma to be higher than those predicted by the commonly used semiempirical formula. Through solving the rate equations, we attribute the enhancement to the target density effects, which will increase the ionization rates on one hand and reduce the electron capture rates on the other hand. The underlying physics is actually the balancing of the lifetime of excited states versus the collisional frequency. In previous measurement with partially ionized plasma from gas discharge and z pinch to laser direct irradiation, no target density effects were ever demonstrated. For the first time, we are able to experimentally prove that target density effects start to play a significant role in plasma near the critical density of Nd-glass laser radiation. The finding is important for heavy ion beam driven high-energy-density physics and fast ignitions. The method provides a new approach to precisely address the beam-plasma interaction issues with high-intensity short-pulse lasers in dense plasma regimes.